In situ gradient nanoprecipitation enables alloys with record-high as-cast strength-ductility synergy

Direct manufacturing of alloys through casting is economical, user-friendly and conducive to near-net-shape processing, and therefore of great application interest. However, as-cast alloys are rarely used directly because, without post-cast thermomechanical treatments, the solidification product is susceptible to coarse grains, compositional segregation and particularly unsatisfying precipitates, which tend towards inadequate strength and brittleness. These ubiquitous disadvantages have, for a long time, seriously hindered practical applications. Here, through screening by using thermodynamic calculations and calorimetric monitoring, we successfully landed non-equiatomic NiCoCrAlTaZrB complex-concentrated alloys (CCAs) to realize in situ micro-segregation-induced size-gradient L1₂ nanoprecipitates increasing from dendritic to interdendritic regions. Consequently, without any post-cast treatment, prolific in situ nanoprecipitation strengthening renders ultrahigh as-cast yield strength at the gigapascal (GPa) level, while multiscale chemical/structural segregation heterogeneities reinforced by gradient nanoprecipitates result in progressive and persistent hetero-deformation within dendrites, thereby sustaining a high strain-hardening rate of ∼3 GPa and uniform tensile elongation of up to ∼32%. Such robust as-cast strength-ductility synergy not only exceeds all previous as-cast CCAs, but also outperforms all commercial alloys that have already been optimized via post-cast treatments. This advance through exploiting in situ size-gradient nanoprecipitation accomplishes a goal that is more practical than the common pursuit for property records, which all require downstream (multistep and/or subtractive) processing that increases production time and expenses, and even raises severe environmental concerns.